Aguirre Pedro A, Lagos Carolina A, Moya Sergio A, Zúñiga César, Vera-Oyarce Cristian, Sola Eduardo, Peris Gabriel, Bayón J Carles
Universidad de Chile, Facultad de Ciencias Químicas y Farmacéuticas, Departamento de Inorgánica y Analítica, Casilla 233 Santiago 1, Chile.
Dalton Trans. 2007 Dec 14(46):5419-26. doi: 10.1039/b704615b. Epub 2007 Sep 25.
The methoxycarbonylation of alkenes catalyzed by palladium(II) complexes with P,N-donor ligands, 2-(diphenylphosphinoamino)pyridine (Ph2PNHpy), 2-[(diphenylphosphino)methyl]pyridine (Ph2PCH2py), and 2-(diphenylphosphino)quinoline (Ph2Pqn) has been investigated. The results show that the complex [PdCl(PPh3)(Ph2PNHpy)]Cl or an equimolar mixture of [PdCl2(Ph2PNHpy)] and PPh3, in the presence of p-toluensulfonic acid (TsOH), is an efficient catalyst for this reaction. This catalytic system promotes the conversion of styrene into methyl 2-phenylpropanoate and methyl 3-phenylpropanoate with nearly complete chemoselectivity, 98% regioselectivity in the branched isomer, and high turnover frequency, even at alkene/Pd molar ratios of 1000. Best results were obtained in toluene-MeOH (3 : 1) solvent. The Pd/Ph2PNHpy catalyst is also efficient in the methoxycarbonylation of cyclohexene and 1-hexene, although with lower rates than with styrene. Related palladium complexes [PdCl(PPh3)L]Cl (L = Ph2PCH2py and Ph2Pqn) show lower activity in the methoxycarbonylation of styrene than that of the 2-(diphenylphosphinoamino)pyridine ligand. Replacement of the last ligand by (diphenylphosphino)phenylamine (Ph2PNHPh) or 2-(diphenylphosphinoaminomethyl)pyridine (Ph2PNMepy) also reduces significantly the activity of the catalyst, indicating that both the presence of the pyridine fragment as well as the NH group, are required to achieve a high performing catalyst. Isotopic labeling experiments using MeOD are consistent with a hydride mechanism for the [PdCl(PPh3)(Ph2PNHpy)]Cl catalyst.
对钯（II）与P，N供体配体（2-（二苯基膦基氨基）吡啶（Ph2PNHpy）、2-[(二苯基膦基)甲基]吡啶（Ph2PCH2py）和2-（二苯基膦基）喹啉（Ph2Pqn）形成的配合物催化烯烃的甲氧基羰基化反应进行了研究。结果表明，配合物[PdCl(PPh3)(Ph2PNHpy)]Cl或[PdCl2(Ph2PNHpy)]与PPh3的等摩尔混合物，在对甲苯磺酸（TsOH）存在下，是该反应的有效催化剂。该催化体系能将苯乙烯高效转化为2-苯基丙酸甲酯和3-苯基丙酸甲酯，化学选择性几乎达到完全，支链异构体的区域选择性为98%，周转频率高，即使在烯烃与钯的摩尔比为1000时也是如此。在甲苯 - 甲醇（3:1）溶剂中得到了最佳结果。Pd/Ph2PNHpy催化剂在环己烯和1-己烯的甲氧基羰基化反应中也有效，尽管反应速率比苯乙烯的低。相关的钯配合物[PdCl(PPh3)L]Cl（L = Ph2PCH2py和Ph2Pqn）在苯乙烯的甲氧基羰基化反应中的活性低于2-（二苯基膦基氨基）吡啶配体。用（二苯基膦基）苯胺（Ph2PNHPh）或2-（二苯基膦基氨基甲基）吡啶（Ph2PNMepy）取代最后一种配体也会显著降低催化剂的活性，这表明吡啶片段和NH基团的存在对于获得高性能催化剂都是必需的。使用MeOD进行的同位素标记实验与[PdCl(PPh3)(Ph2PNHpy)]Cl催化剂的氢化物机理一致。
